System and method for synchronizing wireless communication devices

ABSTRACT

According to the present invention, Bluetooth master device offset information is determined and distributed among the master devices within a Bluetooth network. The system either provides an offset to each master device or determines master device offsets and distributes this information to master devices within the system to allow or efficient hand-offs of a slave between master devices.

BACKGROUND

1. Field

The present invention relates generally to wireless communications, andmore specifically to synchronizing the timing of wireless communicationdevices.

2. Background

In today's electronically interconnected world, the normal complement ofelectronic equipment in the home or business includes devices that areconnected to one another in different ways. For example, many desktopcomputer systems have a central processing unit (CPU) connected to amouse, a keyboard, a printer and so on. A personal digital assistant(PDA) will normally connect to the computer with a cable and a dockingcradle. A television may be connected to a VCR and a cable box, with aremote control for all three components. A cordless phone connects toits base unit with radio waves, and it may have a headset that connectsto the phone with a wire. In a stereo system, the CD player, tape playerand record player connect to the receiver, which connects to thespeakers. These connections can be difficult to install and maintain,particularly for the lay user.

Alternatives to these conventional approaches to connectivity have beenproposed. Bluetooth™ (BT) is a computing and telecommunications industryspecification for connectivity that is both wireless and automatic, asdescribed in The Specification of the Bluetooth System, Version 1.1,Feb. 22, 2001, (“the BT specification”), which is incorporated herein byreference. BT allows any sort of electronic equipment—from computers andcell phones to keyboards and headphones—to make its own connections,without wires, cables or any direct action from a user. Because BTconnections are wireless, offices can be designed without regard tocable placement and users can travel with portable devices withouthaving to worry about carrying a multitude of cables. These connectionscan be established automatically, where BT devices find one another andform a connection without any user input at all.

BT requires that a low-cost microchip transceiver be included in eachdevice. The BT microchip transceiver communicates on a frequency of 2.45GHz, which has been set aside by international agreement for the use ofindustrial, scientific and medical devices (ISM). In addition to data,up to three voice channels are available. Each BT device has a unique48-bit device address from the Institute of Electrical and ElectronicsEngineers 802 standard. Connections can be point-to-point ormulti-point. Data can be exchanged at a rate of 1 megabit per second (upto 2 Mbps in the second generation of the technology).

A number of common consumer devices also take advantage of the same RFband. Baby monitors, garage-door openers and some cordless phones allmake use of frequencies in the ISM band. The BT design employs varioustechniques to reduce interference between these devices and BTtransmissions. For example, BT avoids interfering with other systems bysending out relatively weak signals of 1 milliwatt. By comparison, somecell phones can transmit a signal of 3 watts. The low power limits therange of a BT device to about 10 meters, thereby reducing theprobability of interference with other devices.

BT also employs a spread-spectrum frequency hopping scheme to furtherreduce interference and increase capacity. BT devices use 79 randomlychosen frequencies within a designated range, changing from one toanother on a regular basis 1,600 times every second. The randomfrequency hopping pattern makes it unlikely that two BT transmitterswill be on the same frequency at the same time, thus reducing theprobably of BT devices interfering with one another. This technique alsominimizes the risk that other non-BT devices such as portable phones orbaby monitors will disrupt BT devices since any interference on aparticular frequency will last only a fraction of a second.

When BT devices come within range of one another, an electronicconversation takes place to determine whether they have data to share orwhether one needs to control the other. Once the conversation hasoccurred, the devices form a Personal-Area Network (PAN) or “piconet”. Apiconet may link devices located throughout a room, such as a homeentertainment system, or devices much closer together such as a mobilephone on a belt-clip and a headset, or a computer, mouse, and printer.Once a piconet is established, the connected devices randomly hopfrequencies in unison to communicate with one another and avoid otherpiconets that may be operating nearby.

In the piconet configuration, the connected devices act as eithermasters or slaves, and one master device may control multiple slaves,and, indeed, a master device may, itself, be a slave to another masterdevice.

This master-slave configuration requires that the slave reactsubserviently to its master device, and one way that this occurs isthrough establishing appropriate timing. Specifically, a slave devicemust synchronize its timing with that of its master. Thus, if twoslaves, for example, are in communication with the same master device,they both synchronize their timing with that of the master device.

If, however, a slave moves from one master device to another (referredto hereinafter as “handoff”), the slave device must synchronize itstiming with the timing of its new master device. Since the slave hasbeen communicating with the old master using the old master's timing,and is familiar only with this timing, the new master device must“speak” to the slave in the old master's timing. The new master devicedoes this to notify the slave of the new master's timing information sothat the slave may synchronize to it. In order for this to happen, thenew master device needs to obtain the old master device's timing. The BTSpecification, however, does not specify a procedure for providing thetiming from one master device to another to effectuate an efficienthandoff.

There is therefore a need for an improved system and method forproviding timing information to master devices so that handoffs can beaccomplished efficiently.

SUMMARY

Embodiments disclosed herein address the above stated needs by providinga system and method for the distribution of BT master device timingoffset information within a BT system. According to a first aspect ofthe present invention, BT master device local clocks are generated basedon a free-running global clock and timing offset information. Accordingto a second aspect of the present invention offset information isdistributed among BT master devices that generate their own localclocks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example BT communications environment within which thepresent invention operates.

FIG. 2 illustrates handoff of a slave device between master devices.

FIG. 3 is a schematic representation of a BT master device in moredetail, wherein BT master devices are coupled to a global clock via acommunication pathway.

FIG. 4 is a schematic representation of a BT master device according toan example embodiment of the present invention, wherein an offset isadded to the global clock to create a local clock.

FIG. 5 is a schematic representation of another example embodiment ofthe present invention, wherein offsets are provided by an offsetcontrol.

FIG. 6 is a flowchart that describes a method according to an exampleembodiment of the present invention for operation in a localized BTnetwork.

FIG. 7 is a schematic representation of yet another example embodimentof the present invention, wherein an offset is determined at each masterdevice using a global clock and a local clock generated at the masterdevice.

FIG. 8 depicts an example embodiment of the present invention shown inFIG. 7, wherein offset information is stored in an offset informationstorage.

FIG. 9 is a flowchart that describes a method according to an exampleembodiment of the present invention for operation in a distributed BTnetwork.

DETAILED DESCRIPTION Overview

The present invention relates generally to clock synchronization of BTdevices. According to various example embodiments of the presentinvention, the timing information of BT master devices is distributed toother master devices within the system to facilitate slave devicehandoff between master devices.

FIG. 1 depicts an example BT communications environment 100 according toan example embodiment of the present invention. Example BTcommunications environment 100 includes two or more BT devices 102(shown as 102A, 102B, 102C, and 102D) that communicate with each othervia a wireless link 110 (shown as 110A, 110B, and 110C). In FIG. 1, BTdevices 102A, 102B, and 102C are in communication and form piconet 102A,while devices 102A and 120D form piconet 120B.

BT device 102 represents any device having BT capability according tothe BT Specification. These devices can include, but are not limited to,mobile phones, laptop computers, desktop computers, printers, monitors,keyboards, PDAs, pagers, facsimile machines, and scanners. These devicescan, for example, be equipped with a card or chip that provides BTcommunications capability.

Wireless link 110 represents any type of wireless communication medium.According to an example embodiment of the present invention, wirelesslink 110 represents a wireless radio frequency (RF) link wherein theconnection is established and information is exchanged according to theBT Specification.

In this example BT network 100, BT device 102A acts as a master deviceto BT devices 102B, and 102C, which are slaves. As such, BT devices 102Band 102C synchronize their timing to that of BT device 102A. BT device102A communicates with BT devices 102B and 102C via wireless links 110Band 110C, respectively.

In example BT communication environment 100, BT devices 102 may act as amaster in one piconet 120, yet be a slave in another. This isillustrated in FIG. 1 in that BT device 102A acts as a master of BTdevices 102B and 102C in piconet 120A, yet it acts as a slave to BTdevice 102D in piconet 1208. Consequently, in piconet 120B, BT device102A synchronizes its timing to that of BT device 102D to facilitatecommunication among the devices. This communication occurs acrosswireless link 110A.

FIG. 2 depicts a second example communications environment 200 accordingto the present invention illustrating handoff of a slave device from onemaster device to another. As shown in FIG. 2, a first piconet 120Cincludes a master device 202A in communication with two slave devices208A and 208B via wireless links 110D and 110E, respectively. A secondpiconet 120D includes a master device 202B in communication with a slavedevice 208C via a wireless link 110F.

Master device 202 and slave device 208 represent devices acting in therole of master and slave as described in the BT Specification. They havebeen labeled master and slave devices here for illustrative purposes.Master device 202A acts as a master device to slave devices 208A and208B. Consequently, slave devices 208A and 208B synchronize their timingto that of master device 202A. Once slave devices 208A and 208B havesynchronized their timing to master device 202A, master device 202A maycommunicate with slave devices 208A and 208B via wireless link 110D and110E, respectively.

Similarly, master device 202B acts as a master to slave device 208C. Asa result, slave device 208C synchronizes its timing to that of masterdevice 202B to facilitate communication between the devices via wirelesslink 110F.

Now assume that slave device 208B is handed off from master device 202Ato master device 202B. This handoff may stem from a number of causes.Slave device 208B may move or be moved out of master device 202A'stransmit range into that of master device 202B, wireless link 110E mayfail or be broken somehow, or master device 202A may itself fail or shutdown.

Because master device 202B will now act as the master to slave device208B, slave device 208B will have to synchronize its timing to that ofmaster device 202B. However, up to this point in the handoff, slavedevice 208B has communicated with master device 202A using master device202A's timing information. Consequently, this is the only timing madeknown to slave device 208B. Therefore, to facilitate the handoff, masterdevice 202B initially communicates with slave device 208B using thetiming of master device 202A. It does this to let slave device 208B knowthat slave device 208B now needs to synchronize its timing to the timingof master device 202B.

In order to complete the handoff, master device 202B should thereforeobtain the timing information of master device 202A. Upon acquiring thisinformation, master device 202B establishes wireless link 110G using thetiming of master device 202A. Slave device 208B successfully receivesthis message because it is in the timing of its old master, i.e. masterdevice 202A. Master device 202B then informs slave device 208B of masterdevice 202B's timing, and slave device 208B synchronizes its timing tothat of master device 202B. As a result, piconet 120D expands to includemaster device 202B, and slave devices 208B and 208C. Conversely, piconet220A shrinks to include only master device 202A and slave device 208A.

Therefore, handoff efficiencies increase when, in a handoff situation,the new master device is aware of or has access to the timinginformation of the old master device so that the new master device mayinitially communicate with the handed-off slave device using the oldmaster's timing.

FIG. 3 is an example configuration 300 showing this timing informationaccording to an example embodiment of the present invention. The exampleconfiguration 300 includes a global clock 306, which is delivered via acommunication pathway 304 to two or more master devices 202 (shown as202C and 202D). Each master device 202 includes a local clock 310 (shownas 310A and 310B) and an offset 308 (shown as 308A and 308B).

In an example embodiment of the present invention, global clock 306 canrepresent a stand-alone free running clock. However, those of skill inthe art will recognize that global clock can also be implemented usingthe local clock of one of the master devices 202 within exampleconfiguration 300.

Offset 308 represents a phase difference between global clock 306 and alocal clock of master device 202. This difference may be predeterminedand constant, or it may be realized by calculating the differencebetween the value of global clock 306 and that of an independent localclock of master device 202. When offset 308 is predetermined andconstant, this predetermined value is used along with the value ofglobal clock 306 to generate a local clock for master device 202. Forexample, the offset can be used to adjust the phase of the global clock.In the systems that implement clocks as an integer count, such asdescribed in the BT Specification, the offset can be added to orsubtracted from the current count to achieve a phase shift.

Communication pathway 304 represents any communication medium. Thisincludes wired communication media such as a bus architecture orwireless media such as RF or infrared transmissions.

To reduce the possibility of interference, offset 308 is typicallydifferent in value from one master device 202 to another. For exampleoffset 308A of master device 202A has a different value than offset 308Bof master device 202B. This uniqueness of offset 308 preventsinterference in the transmissions of master devices 202A and 202B.

According to various example embodiments of the present invention,efficient handoffs are facilitated by distributing offsets 308 viacommunication pathway 304 so that each master device 202 knows theoffset 308 of other master devices 202 and can therefore communicatewith a new slave in the old master device's timing. The followingdiscussion will describe example embodiments of the present inventionregarding the creation and distribution of offsets 308 in variousnetwork configurations. Specifically, the discussion will describeexample embodiments of the present invention in terms of localizednetworks and distributed networks. Localized networks are networks inwhich master devices are physically located in close proximity to oneanother, for example, in a rack configuration. Conversely, distributednetworks are those in which master devices are located in differentgeographic areas, for example, in different buildings on a collegecampus.

Localized Networks

FIG. 4 shows an example master device 202 in greater detail according toan example embodiment of the present invention. Master device 202includes a control block 408, and an adder 404 to combine global clock306 with offset 308 to form local clock 310. Local clock 310 in thisexample embodiment is derived using global clock 306 and offset 308 inthat offset 308 is combined with global clock 306 to produce local clock310. Adder 404 represents any mechanism, including hardware, software,or a combination of hardware and software for combining the value ofglobal clock 306 with that of offset 308. As mentioned above, thecombination of these values produces local clock 310 which is aphase-shifted version of global clock 306. Control block 408 representsa mechanism for controlling the communication activities of masterdevice 202 in accordance with the BT Specification.

In this example, global clock 306 is input to master device 202 viacommunication pathway 304. Offset 308 is then combined by adder 404 withglobal clock 306 to create local clock 310. As described above, anyslave device 208 in communication with master device 202 will have tosynchronize its timing with local clock 310. The value of offset 308 canbe unique to master device 202, 268 and may, in particular exampleembodiments according to the present invention, be predetermined andconstant.

FIG. 5 illustrates an example network 500 having an offset control 502and an offset communication pathway 508 added to configuration 400.Offset control 502 provides values of offsets 308, via offset pathway508, to master devices 202. Offset control may be implemented ashardware, software, or any combination of hardware and software and maybe located or stored at a remote location accessible via offsetcommunication pathway 508 or within a master device 202. Offsetcommunication pathway 508 represents any communication medium, includingwired and/or wireless communication connections. Those of skill in theart will recognize that communication pathway 304 may also perform thefunctionality of offset communication pathway 508.

According to an example embodiment of the present invention, examplenetwork 500 is made up of master devices 202 in a localized network,that is, located in relatively close physical proximity, as in a rackconfiguration. Here, communication pathway 304 and offset communicationpathway 508 can be implemented using, for example, a bus or other wireline connection. Further, master devices 202, global clock 306, andoffset control 502 can be implemented, for example, as one or more cardsplugged into the bus. Offset control 502 establishes offsets 308A and308B for master devices 202A and 202B, respectively, and distributesthem to master devices 202A and 202B. The value of offset 308A isdifferent from that of offset 3088. As was described above withreference to FIG. 4, global clock 306 is input to each master device 202via communication pathway 304.

As shown in FIG. 5, adders 404A and 404B combine offsets 308A and 308Bwith global clock 304. This combination creates local clocks 310A and310B, which also have different values because of the different valuesof offsets 308A and 3088. As described above, any slave devices 208 incommunication with master devices 202A and 202B will have to synchronizetheir timing with local clock 310A and 310B, respectively. Since offsetcontrol 502 determines offsets 308 for each of master devices 202, itknows the value of offsets 308 for each of the master devices 202.Therefore, when master device 202A, for example, needs offset 308B ofmaster device 202B, to, for example, effect a handoff, master device202A can receive the necessary offset information from offset control502. Those of skill in the art will recognize that offset control 502may distribute offset 308 of one master device 202 to another in anumber of ways. For example, offset control 502 can provide offset 308of one master device 202 to another when master device 202 requests theinformation. Or, offset control 502 can inform master devices 202 ofoffsets 308 of other master devices 202 when providing master device 202with its particular offset 308.

FIG. 6 is a flowchart 600 that describes the operation of an exampleembodiment of the present invention in which local clock 310 of eachmaster device 202 is derived by adding offset 308 to global clock 306.In operation 602, global clock 306 is distributed to master devices 202.As shown in FIGS. 3, 4, and 5, global clock 306 is distributed to masterdevices 202 via communication pathway 304.

In operation 604, offset 308 is added to global clock 306 to createlocal clock 310 used by master device 202. As shown in FIGS. 4 and 5,adder 404 combines global clock 306 and offset 308 to generate localclock 310. FIGS. 4 and 5 also show that offset 308 is distributed tomaster devices 202 from offset control 502 via offset communicationpathway 508.

In operation 606, offset 308 is distributed to at least one masterdevice 202. This distribution allows master devices 202 to efficientlyacquire offset 308 of other master devices 202 when handoff of a slavedevice from one master device 202 to another is required.

Referring back to FIG. 2, this method will allow efficient hand off ofslave device 208B from master device 202A to master device 202B. This istrue because offset 308A of master device 202A will be distributed tomaster device 202B so that this new master device will be able tocommunicate to slave device 208A to inform it that it needs to nowsynchronize its timing to that of master device 202B. As describedabove, this distribution may be done in a number of ways.

The configuration of FIG. 4 allows the use of a single global clock 306to create local clocks 310. This is because the master devices 202 arein close proximity of global clock 306 and distribution of global clock306 to the master devices 202 is less hindered by distance.

Distributed Networks

The previous embodiments are most applicable to localized networks inwhich the master devices are in relatively close physical proximity.FIG. 7 depicts a network 700 according to an example embodiment of thepresent invention that may be used in distributed networks in whichmaster devices 202 are located remotely from one another. In thisexample embodiment, each master device 202 includes a local clockgenerator 704 (shown as 704A and 704B), local clock 310 (shown as 310Aand 310B). Local clock 310 is compared with global clock 306 todetermine offset 308 (shown as 308A and 308B).

Local clock generator 704 represents a clocking mechanism that generateslocal clock 310 for a particular master device 202. Those of skill inthe art will recognize that local clock 310 can be implemented as acrystal oscillator that runs independent of global clock 306.

According to the exemplary embodiment of FIG. 7, global clock 306 is fedinto master devices 202A and 202B as previously described with referenceto FIGS. 4 and 5. However, unlike the configuration of FIGS. 4 and 5,each master device 202 generates its own local clock 310 independentfrom global clock 306. This is possible because each master device 202has its own crystal oscillator generating its unique local clock 310.Then, based on local clock 310 and global clock 306, each master device202 determines its offset 308 by calculating the difference betweenglobal clock 306 and its own local clock 310. Local clock generator 704will, in all likelihood, generate a local clock having a phase differentfrom that of local clock 310B. Consequently, offset 308A will bedifferent from offset 308B. Recall that interference is minimized whenoffsets 308 of master devices are different from one another. Thus, inthis example embodiment of FIG. 7, as with the example embodimentpreviously described with reference to FIGS. 4 and 5, each offset 308should be unique to each master device 202.

FIG. 8 depicts a more detailed representation of master device 202 ofFIG. 7. As shown, master device 202 includes localized offsetinformation storage 802 and central offset storage 810.

Offset information storage 802 represents memory for storing the offsets308 from other master devices 202 in network 800. As described above,this offset information is used by master device 202 when effecting ahandoff. Offset information storage 802 can be used to store aparticular offset 308 that is requested by a master device when neededto complete a handoff. Offset information storage 802 can also be usedto store offsets 308 corresponding to one or more other master deices202 that is stored locally for convenient accessibility if needed for afuture handoff. Offset information storage 802 may be implemented usinghardware, software, or any combination of hardware or software.

Similarly, central offset storage 810 may be used in lieu of or inaddition to offset information storage 802 to store offset informationof master devices 202 for distribution or retrieval by master devices202 involved in a handoff. It, too, may be implemented using hardware,software, or a combination of hardware and software.

In this example embodiment of the present invention, offset 308 may bedistributed, via offset communication pathway 508, in a number of ways.For example, master device 202 may intermittently post its offset 308 onoffset communication pathway 508 and intermittently retrieve offsets 308for the other master devices 202 and store this information in localizedoffset storage bank 802. This allows master devices 202 to possessoffsets 308 of other master devices which facilitates efficient handoffsshould the need arise.

In addition to this form of distribution, offset 308 may be stored incentral offset storage and retrieved on demand, i.e., master device 202will post its offset 308 for retrieval by another master device onlywhen the retrieving master device requests it. Also, rather than eachmaster device 202 storing offset 308 information for all other masterdevices, this information could be stored in a central location on thenetwork. Also, rather than intermittently posting and retrieving offsets308, this could be done on a continuous basis.

FIG. 9 is a flowchart 900 describing the operation of an exampleembodiment of the present invention in which each master device 202 in anetwork has its own local clock 310. In operation 902, global clock 306is distributed to two or more master devices 202. As shown in FIGS. 7and 8, this distribution is via communication pathway 304 and may bedone in a number of ways. In operation 904, offset 308 is determined bycalculating the difference between global clock 306 and local clock 310.This may be done using adder 404 as shown in FIG. 8. In operation 906,offset 308 is distributed to at least one of the plurality of masterdevices 202. As mentioned above, this distribution may be done in anumber of ways, and as shown in FIGS. 7 and 8, is carried out overoffset communication pathway 508.

As mentioned above, this example embodiment of the present invention ismost applicable to a distributed network. In the configuration of FIG.9, master devices 202 are distributed over a geographical area such as acollege campus, a shopping mall, or a business facility. Master devices202 generate their own local clock 310 and offset 308 based on thedifference between global clock 306 and their local clock 310. Themaster devices 202 then distribute their offset 308 to other masterdevices 202 in the manner described above. This distribution istypically done via offset communication pathway 508, or may be done viacommunication pathway 304. Communication pathway 304 and offsetcommunication pathway 508 may be implemented as a wired network or as awireless network, and can be implemented as a single or multiplenetworks. The distribution described above allows for efficient handoffswhen a slave device 208 moves from, for example, one area of thedistributed network to another, for example.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1-30. (canceled)
 31. A method for distributing timing information amonga plurality of master devices, comprising: receiving a global clock byeach master device of the plurality of master devices, wherein eachmaster device comprises a respective wireless communication device,wherein each master device is a respective master of a correspondingwireless network, wherein each master device operates according to arespective and unique local clock that is independent of the globalclock, wherein a slave device wirelessly communicates with a firstmaster device of the plurality of master devices by synchronizing withthe respective local clock of the first master device; determining, ineach master device, a respective offset between the global clock and therespective local clock, wherein the respective offsets are differentfrom each other; and transmitting the respective offset of the firstmaster device of the plurality of master devices to a second masterdevice of the plurality of master devices to facilitate a handoff of theslave device from the first master device that is a master of a firstwireless network to the second master device that is the master of asecond wireless network.
 32. The method according to claim 31, whereinthe global clock comprises a local clock of another master device. 33.The method according to claim 31, wherein the respective offset of thefirst master device is distributed over a communication pathway linkingthe first master device to the second master device.
 34. The methodaccording to claim 33, wherein the communication pathway comprises awired communication pathway.
 35. The method according to claim 33,wherein the communication pathway comprises a wireless communicationpathway.
 36. The method according to claim 31, wherein each masterdevice transmits the respective offset to a network storage device, andwherein each master device can request, from the network storage device,the respective offsets of other master devices of the plurality ofmaster devices.
 37. The method according to claim 31, wherein the secondmaster device requests the respective offset of the first master device,and wherein the first master device transmits the respective offset tothe second master device.
 38. The method according to claim 31, whereineach master device stores respective offsets of other master devices ofthe plurality of master devices to effect handoffs of slave devices. 39.The method according to claim 31, wherein the first master devicecomprises a first mobile phone, and wherein the second master devicecomprises one or more of the following: a second mobile phone, apersonal digital assistant, a printer, and a computer.
 40. A method fordistributing timing information amongst of a plurality of masterdevices, comprising: receiving a global clock by each master device ofthe plurality of master devices, wherein each master device comprises arespective wireless communication device, and wherein each master is arespective master of a corresponding wireless communication network;transmitting, to each master device, a respective and unique offset;generating, in each master device, a respective local clock using therespective offset and the global clock, wherein the respective localclock is used by a first master device of the plurality of masterdevices to wirelessly communicate with a slave device in the respectivewireless communication network of the first master device; andtransmitting the respective offset of the first master device to asecond master device of the plurality of master devices to facilitate awireless handoff of the slave device from the first master device thatis a master of a first wireless communication network to the secondmaster device that is the master of a second wireless communicationnetwork.
 41. The method according to claim 40, wherein each of themaster devices comprises a local oscillator, and wherein the globalclock comprises a clock signal generated by the local oscillatorassociated with one of the plurality of master devices.
 42. The methodaccording to claim 40, wherein the respective offsets are stored in anetwork element and provided to at least two of the master devices. 43.The method according to claim 40, wherein the respective offset of thefirst master device is stored locally at the second master device. 44.The method according to claim 40, wherein the first master devicecomprises a first mobile phone, and wherein the second master devicecomprises one or more of the following: a second mobile phone, apersonal digital assistant, a printer, and a computer.
 45. Acommunication system, comprising: a global clock transmitting, over afirst communication pathway, a global clock signal to each master deviceof a plurality of master devices; and each master device of theplurality of master devices comprising a respective local clockgenerator that generates a respective and unique local clock and arespective memory that stores a respective offset, wherein each masterdevice determines the respective offset from the global clock and therespective local clock, wherein each master device comprises arespective wireless communication device, wherein each master is arespective master of a corresponding wireless communication network,wherein a first master device of the plurality of master devicestransmits, over a second communication pathway, its respective offset toa second master device of the plurality of master devices to facilitatea wireless handoff of a slave device from the first master device thatis a master of a first wireless communication network to the secondmaster device that is the master of a second wireless communicationnetwork, wherein the slave device is synchronized with the respectivelocal clock of the first master device, and wherein the respectiveoffset of the first master device is used by the second master device tocommunicate with the slave device.
 46. The system according to claim 45,wherein the first communication pathway comprises a first wirelesscommunication pathway, and wherein the second communication pathwaycomprises a second wireless communication pathway.
 47. The systemaccording to claim 45, wherein the respective offsets of the pluralityof master devices are stored in a network storage device.
 48. The systemaccording to claim 45, wherein the global clock comprises one of therespective local clocks of the plurality of master devices.
 49. Thesystem according to claim 45, wherein the second master device requeststhe respective offset of the first master device, stores the respectiveoffset of the first master device in the respective memory of the secondmaster device, and uses the respective offset of the first master deviceto communicate with the slave device.
 50. The system according to claim45, wherein the respective offsets are distributed by a network storagedevice upon request by one of the master devices.
 51. The systemaccording to claim 45, wherein the respective memory of the secondmaster device stores the respective offset of the first master deviceand the respective offsets of other master devices of the plurality ofmaster devices.
 52. The system according to claim 45, wherein the firstmaster device comprises a first mobile phone, and wherein the secondmaster device comprises one or more of the following: a second mobilephone, a personal digital assistant, a printer, and a computer.
 53. Acommunication system, comprising: a global clock that transmits, over afirst communication pathway, a global clock signal to each master deviceof a plurality of master devices, wherein each master device comprises arespective wireless communication device, and wherein each master deviceis a respective master of a corresponding wireless communicationnetwork; and an offset controller that transmits, over a secondcommunication pathway, a respective and unique offset signal to eachmaster device, wherein each master device comprises a respective localclock generator that generates a respective local clock signal as afunction of the respective offset signal and the global clock signal,wherein the respective local clock signal of a first master device ofthe plurality of master devices is used by the first master device tosynchronize communication with a slave device, and wherein therespective offset signal of the first master device is transmitted to asecond master device of the plurality of master devices to facilitate awireless handoff of the slave device from the first master device thatis a master of a first wireless communication network to the secondmaster device that is the master of a second wireless communicationnetwork.
 54. The system according to claim 53, wherein the firstcommunication pathway comprises a first wired communication pathway, andwherein the second communication pathway comprises a second wiredcommunication pathway.
 55. The system according to claim 53, wherein thefirst communication pathway comprises a first wireless communicationpathway, and wherein the second communication pathway comprises a secondwireless communication pathway.
 56. The system according to claim 53,wherein the global clock generates a single global clock signal that isused by each master device, and wherein the single global clock signalis generated by one of the clock generators of the plurality of masterdevices.
 57. The system of claim 53, further comprising a memory that isoperatively coupled to the second communication pathway, wherein theoffsets are stored in the memory.
 58. The system according to claim 53,wherein each master device receives the respective offset for each ofthe other master devices.
 59. The system according to claim 53, whereineach of the master devices comprises a local memory for storing offsetsassociated with at least one of the master devices.
 60. The systemaccording to claim 53, wherein the first master device comprises a firstmobile phone, and wherein the second master device comprises one or moreof the following: a second mobile phone, a personal digital assistant, aprinter, and a computer.
 61. The method according to claim 40, whereinthe respective offsets of the plurality of master devices arepredetermined and constant.
 62. The system according to claim 53,wherein the first communication pathway comprises a bus that isoperatively coupled to a first card and to a second card, wherein thefirst master device is part of the first card, and wherein the secondmaster device is part of the second card.
 63. The system according toclaim 45, wherein each master device intermittently posts the respectiveoffset on the second communication pathway, and wherein each masterdevice intermittently receives, via the second communication pathway,the respective offsets of the other master devices of the plurality ofmaster devices.
 64. The method according to claim 31, wherein eachmaster device intermittently transmits the respective offset andintermittently receives the respective offsets of the other masterdevices of the plurality of master devices.